Rotary screen printing cylinder having separated ink zones

ABSTRACT

A rotary screen printing cylinder including a cylindrical screen, a squeegee disposed within the screen, and two end pieces each fastened as an extension of the cylindrical surface of the screen. The screen cylinder has at least two zones which are provided with color-permeable openings at least in partial areas and are separated by a color-impermeable dead zone of predetermined width. The dead zone is designed so as to give the screen cylinder stability.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary screen printing cylindercomprising a cylindrical screen having at least one zone provided withcolor-permeable openings at least in partial areas, a squeegee disposedwithin the screen, and two end pieces each fastened to an end of thescreen as an extension of the cylindrical surface. The invention relatesfurther to a system of such rotary screen printing cylinders and to amethod for producing them.

2. Description of the Prior Art

In screen process printing, the color is pressed with the help of asqueegee through a stretched screen surface, generally a plastic ormetal fabric of predetermined mesh width, the fabric being impervious tocolor in the nonprinting areas. The pores are usually blockedphotographically by the screen material being coated with a photographicemulsion and exposed to the desired composition pattern. The exposedareas are washed away during the subsequent development of the emulsionso that the screen becomes color-permeable on the exposed areas.

Originally a screen printing unit comprises a metal or wooden frame overwhich the screen material is stretched without deformation. Due to theeconomic necessity of producing faster and more efficient printingmachines one has developed rotary screen printing units which allowcontinuous printing of endless sheets. The screen is no longer flat butformed as a cylinder envelope inside which the color squeegee isfastened.

The cylindrical screen is produced for example by accordingly shaping aplastic or metal fabric which is subsequently welded along thecylindrical surface. However this weld causes problems during printing,so that rotary screen printing cylinders are very frequentlyelectroplated as this production process obtains a uniform screensurface.

EP 0 164 149 describes such a production method. In this method anelectroconductive screen master is placed in an electrolytic bath andconnected with the cathode of a current transmitter. A metal layer isthen deposited on the master, which is subsequently removed from themaster and patterned. Prior to patterning the screen material has auniform perforation which must be made color-impermeable in thenonprinting areas for printing. This is usually done with the help ofthe abovementioned photographic methods.

EP 0 338 612 A1 describes, for example, such a method for rotary screenprinting cylinders. The screen likewise consists in this case of aperforated metal cylinder to which an end piece is glued as an extensionof the cylindrical surface in each case prior to patterning. The rigidlymounted end pieces allow easy and quick replacement of the printingcylinder in the printing unit, which is of great benefit particularlywith small print orders. Only after the connecting elements are glued tothe screen is the latter coated with the photographic emulsion andexposed in the usual way. As soon as a new printing pattern is requiredthe unexposed photographic emulsion, which blocks the nonprinting areasof the uniformly perforated screen, can be removed and the screen coatedand exposed again.

The resolution in screen printing depends solely on the mesh width andthe thread or wire thickness of the screen. The finer-meshed the screenis, the greater the resolution is. Since cylindrical screens with meshwidths of approx. 120/cm are used for high resolutions and such a meshfabric is extremely unstable, high-resolution screens can be producedonly with small effective printing widths (so-called working widths) ofless than 60 cm if sufficient stability of the print roll is to beguaranteed.

SUMMARY OF THE INVENTION

The invention is therefore based on the problem of proposing a rotaryscreen printing cylinder which can be produced simply andcost-effectively and nevertheless permits the processing of largeprinting widths.

The invention is based on the idea that the printing areas of the screenare separated from one another by extensive nonprinting dead zones andthese dead zones are designed so that the printing cylinder hassufficient stability.

The screen printing cylinder can be designed in the customary way as auniformly perforated cylinder envelope, with reinforcing rings providedat certain intervals within the cylinder. This reinforced area forms theabovementioned dead zone and must of course not be exposed duringsubsequent patterning, i.e. of color-permeable design. If this measureresults in a gap in the printed image, a second printing cylinder can beproduced for printing in this gap in good register in a second printingoperation and thus completing the printed image.

Another way of giving the printing cylinder stability is to make thecylinder screenlike only in the printing areas. This is of advantage inparticular if the printed image involved is a relatively small one whichrepeats itself several times across the width of the cylinder, as isfrequently the case in the processing of multiple printed sheets. Thesame naturally holds for a plurality of printed images to be applied inseparate places, which might also be printed in different colors.

The screen cylinder is made in this case of an unperforated compact basematerial, such as metal, tin or plastic, which is provided in the zonesintended to be color-permeable with the openings of predetermineddiameter corresponding to the desired printed image. The screen holescan be burned with a laser or etched into the material. It is of courselikewise possible to electroplate the screen. The zones provided withthe color-permeable openings are separated from one another by theunperforated dead zones of base material.

A further inventive embodiment involves producing individual fine-meshedrotary screen printing cylinders with a small printing width andinterconnecting these cylinders along their axis so that almost any webwidth of material to be printed can be processed. For this purpose themetallic end pieces of the printing cylinder, which constitute theconnecting elements for driving the printing unit, are replaced on atleast one side by an accordingly shaped connecting element, e.g. aflange. The first and last printing cylinders of such a row still ofcourse have the corresponding known connection element for driving themachine.

However, a plurality of printing cylinders provided with a flange-shapedend piece on each side can be disposed between these two printingcylinders according to the invention. The nonprinting dead zones in thearea of the flange elements can result in gaps in the printed image, asmentioned above, which can be filled in with the help of a secondprinting cylinder.

An advantage of this embodiment is that the individual printingcylinders can still be produced by standard machines in the customarymanner so that there are no additional costs for elaborate machinechange-overs.

However applications are also conceivable for which an undetachableconnection is advantageous. In this case the end pieces can be forexample simple pipe elements which are firmly welded together.

According to a further embodiment, the connecting elements between thescreen areas can also be manufactured from one piece, so that onebasically has only one screen printing cylinder whose screen area isinterrupted by the supporting connecting elements at certain places.

The individual printing cylinders can of course be designed as desired.For example one of the cylinders can be made of a solid material whichis screenlike only in certain zones, while another is made of a meshfabric patterned in the usual fashion.

The invention accordingly offers the possibility of producing a rotaryscreen printing cylinder of any axial length which has high stabilityindependently of the size of the openings of the printing screen areadue to the reinforced zones. In this way the printing zones of thescreen can be adapted optimally to the requirements, e.g. in terms ofresolution.

The separation into printing color-permeable zones and color-impermeabledead zones further offers the advantage that several colors can beprinted side by side in one printing operation. If the reinforcement ofthe printing zones is formed by separate elements, such as reinforcingrings or flanges, these elements can serve simultaneously as colordividers which prevent the colors from blending.

The inventive rotary screen printing cylinders can furthermore be usedespecially advantageously in security printing. In the production ofbank notes it is frequently necessary to print individual, spaced paperareas with special inks, which contain e.g. fluorescent or magneticsubstances or iridescent pigments. Just one printing cylinder can beused according to the invention for applying these different colorareas. For this purpose the cylinder is divided into a plurality ofcolor-permeable zones which are separated by accordingly designedcolor-impermeable dead zones along the entire cylinder periphery. Thecolor-permeable zones are patterned in accordance with the desiredprinted image and subsequently brought in contact with the particularcolor.

Instead of colors one can of course also print lacquers or adhesives ina certain pattern. For example it is conceivable to apply one or moreeffect colors and a locally limited layer of lacquer or adhesive to theantifalsification paper in one printing operation. A further securityelement, such as a hologram or interference layer element, couldsubsequently be fastened in the area of the adhesive layer.

Further embodiments and advantages of the invention will be explainedwith reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a paper of value with various printed features;

FIG. 2 shows a schematic arrangement of print rolls for screen printing;

FIG. 3 shows a sketch of a screen printing cylinder with a chamber-typesqueegee, in cross section;

FIG. 4 shows a first variant of the inventive screen printing cylinder;

FIG. 5 shows a second variant of the inventive screen printing cylinder;

FIG. 6 shows a longitudinal section through a further variant accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows paper of value 10, e.g. a bank note made ofantifalsification paper, which has several security features 1, 2, 3.Features 1, 2 are printed features which were applied by screenprinting. The inks used for printing these features 1, 2 are subject tono restriction in terms of composition and can contain featuresubstances, such as fluorescent or magnetic pigments, along withcoloring pigments, or only the feature substances dispersed or dissolvedin a binder. It is equally conceivable to use iridescent interferencelayer pigments which show a striking viewing angle-dependent coloreffect. Security feature 3, however, can be a multilayer element, suchas a hologram or coated plastic thread, which is fastened to theantifalsification paper film with the help of a layer of adhesive orlacquer. The antifalsification paper can of course also have othersecurity features, such as an embedded security thread or the like.

FIG. 2 illustrates the principle of screen printing using rotary screenprinting cylinders. A screen printing cylinder 4 is color-permeable onlyin the area of the printing pattern to be transferred, while theremaining part of the screen is color-impermeable. A squeegee 5 isfastened within the printing cylinder 4, and consists generally ofwooden or metal rod 6 extending in the axial direction of the cylinder 4and a rubber or plastic strip, the actual squeegee element 7, fastenedthereto in the radial direction. The squeegee element 7 presses ink 8likewise introduced inside the cylinder 4 through the permeable openingsin the cylinder 4. The ink is transferred to the material 9 to beprinted, e.g. paper or plastic, in the area of a back pressure roll 11.

Instead of strip-shaped squeegee 5 one can also use a chamber-typesqueegee 12 whose mode of operation is illustrated in FIG. 3. Thechamber-type squeegee 12 consists of two rubber or plastic lips 13, 14which lie against the inside of screen printing cylinder 4 and press ink8 through the screen openings. The opposite ends of the lips 13, 14 areconnected with a sealed housing 15 into which ink 8 is pumped via avalve 16 in an electronically regulated fashion.

FIG. 4 schematically shows a patterned rotary screen printing cylinder20 pursuant to the present invention in plan view for applying the inksfor areas 1, 2 shown in FIG. 1 and for the adhesive layer of element 3in just one printing operation. Cylindrical surface 21 is subdividedalong its rotation axis a into color-permeable or at least partlycolor-permeable zones 22 and color-impermeable dead zones 23 disposedtherebetween, which in each case extend over the cylindrical surface inrotationally symmetric fashion. Zones 22, 23 are defined solely by thepresence or absence of color-permeable openings in the cylindricalsurface 21. Dash lines 24 are therefore provided only for clarity's saketo define the zones and are not present on the cylinder 20.

The color-permeable openings in areas 25 constitute the actual screensince only through them can color pass onto the material to be printed.The color-permeable openings can come about in different ways. One canuse for the screen cylinder 20 for example a compact, i.e. as yetunperforated, plastic, metal or tin material in which the desiredopenings are provided by an electronically controlled laser. This hasthe advantage that the size, i.e. diameter, of the openings can bedifferent, so that the resolution and color application can be variedfor different printed images, although they are located on one printingcylinder. In this variant the dead zones 23 consist of unperforatedsolid material, which gives the printing cylinder 20 sufficient strengthso that no additional reinforcing elements are necessary in this area.

The same holds if the cylinder 20 is produced by etching techniques orelectroplating. In the etching technique a metal sheet, for example, isprovided with an acidproof coating which covers all areas except thescreen openings to be produced. The coated sheet is then put in acaustic liquid which attacks and dissolves the exposed uncoated metalsurfaces.

Alternatively one can use a regular mesh fabric, preferably of metalwire, in the usual way. The mesh aperture is generally about 1.5 to 2.5times the wire diameter. FIG. 5 shows a printing cylinder 30 whosesurface is made of a regular mesh fabric, which is omitted in thedrawing for reasons of clarity. The cylindrical surface 31 of thecylinder 30 is likewise subdivided along the rotation axis a intocolor-permeable zones 32 and color-impermeable dead zones 33. The zoneboundaries are again indicated by dash lines 34. The dead zones 33,which likewise have openings in this embodiment, are provided withreinforcing elements, reinforcing rings 35 here, inside the cylinder 30to increase the stability of the cylinder 30. These elements 35 can beworked directly into the material or glued on. During subsequentphotographic patterning of the cylindrical surface 31, the entirecylinder 30 is coated with a photographic emulsion and exposed at leastpartly in the zones 32. The exposed areas are finally washed away sothat the mesh fabric is uncovered and becomes color-permeable in theseplaces.

FIG. 6 shows a further embodiment of the invention. It shows alongitudinal section through two flanged-together rotary screen printingcylinders 40, 50 according to the invention. On the side facing theprinting unit, cylinders 40, 50 have conventional end pieces 41, 42 thatensure the connection to a driving system 43 of the printing unit. Theend pieces 41, 42 are of course also present in the previously-describedembodiments, even if not shown in the figures. The opposite ends of thescreen cylinders 40, 50 are provided with flange elements 44 for theinterconnecting cylinders 40, 50. The flange elements 44 can be equippedwith a washer or guide groove to guarantee that the cylinders arebrought together in exact register. Further printing cylinders can bedisposed between the cylinders 40, 50 as required, being provided withflange elements 44 on each side so they can be connected with thecylinders 40, 50 in the axial direction. The squeegee 45 consists inthis case of one squeegee rod 46 common to all the cylinders 40, 50,which is provided in the area of the individual cylinders 40, 50 withactual squeegee elements 47 which guarantee the ink transfer to thematerial to be printed. The same squeegee assembly can of course be usedin the embodiment described with reference to FIG. 5. A back pressureroll 48 is also arranged to extend over the entire printing width. Inthe flange zone the printing screen consisting of the individual screens40, 50 can be supported by supporting rolls in the printing unit.

Instead of flange elements, which permit an easily detachableconnection, one can also use at any desired place other connectingelements which are less easily, or not at all, detachable. It isconceivable, for example, to provide one or more of the individualprinting cylinders with different end pieces. If, for example, two offour individual cylinders are to be interconnected undetachably, aone-piece connecting element can be provided therebetween, while theconnecting elements with the other two individual cylinders might beformed as flange elements. In this case the first two screen elements,which are connected by the one-piece connecting element, are expedientlyconnected before the screens are patterned since the connecting elementmanufactured from one piece serves both screens as a stabilizing endpiece. The reverse procedure, producing and patterning the screenssingly without the common connecting element and subsequently insertingthe connecting element between the screen elements, might also beappropriate in some cases, however, e.g. if the existing machineequipment for producing the screens is not designed for the length ofthe connected screen elements.

All these embodiments have the great advantage that the individualscreen can be adapted specifically to the required printing quality andthe necessary printing width is obtained by connecting a plurality ofindividual printing cylinders, the connecting elements servingsimultaneously as supporting elements for the assembled printingcylinder. It is thus possible using the invention to produce screenprinting cylinders with a working width of 80 cm or more althoughscreens with mesh widths of approx. 120/cm are used.

Due to the possibility of combining any printing cylinders, it is alsoconceivable to assemble cylinders from individual screens of differentmesh widths. One can likewise combine printing cylinders produced indifferent ways.

The invention further makes it possible to print several colors at thesame time if the color-permeable zones are each brought in contact witha different ink. One must of course make sure the different inks do notmix. If reinforcing elements, such as reinforcing rings or flangeelements, are provided in the nonprinting dead zones, they can functionsimultaneously as color dividers. In the embodiments of FIGS. 5 and 6 itis therefore readily possible to form separate screen chambers in whichthe color can be introduced e.g. by means of separate electric pumpingsystems.

It is also possible to print different colors simultaneously in thevariant of FIG. 4 by providing each color-permeable zone 22 with aseparate chamber-type squeegee.

The invention can furthermore be used favorably wherever colors areprinted very finely and over great widths, such as in the printing ofplastic films which are subsequently cut into narrow bands with a widthin the range of a few millimeters and embedded in antifalsificationpaper as security threads. Such threads very frequently havemicrowriting which must be printed legibly on the wide film sheet atsuitable intervals. Up to now this could only be done by rotogravure,which increased the production costs in view of the complicated andelaborate printing plate production.

The invention can naturally also be used advantageously for printingsecurity documents made of plastic, such as identity cards.

I claim:
 1. A rotary screen printing cylinder, comprising:a cylindricalscreen having a circular cross-section and a cylindrical surface with atleast one color permeable zone provided with color-permeable openings; asqueegee disposed within the screen; and two end pieces respectfullyconnected to opposite ends of the screen as an extension of thecylindrical surface, one of the end pieces being formed so as tostabilize the screen printing cylinder and being further formed as meansfor connecting the one end piece with another screen printing cylinder.2. The rotary screen printing cylinder of claim 1, wherein theconnecting element is a flange element.
 3. The rotary screen printingcylinder of claim 1, wherein the color permeable openings have differentdiameters.
 4. A rotary screen printing cylinder, comprising:acylindrical screen having a circular cross-section and a cylindricalsurface with a fabric of predetermined mesh width; a squeegee disposedwithin the screen; two end pieces respectively connected to oppositeends of the screen as an extension of the cylindrical surface; andarranging at least one reinforcing element on an entire innercircumferential surface of the screen to divide the screen into twoscreen chambers and so as to stabilize the screen printing cylinder, thereinforcing element being configured to occupy only a portion of thecircular cross-section and axial extension of the screen.
 5. A systemcomprising a plurality of axially connected rotary screen printingcylinders, each of the rotary screen printing cylinders comprising acylindrical screen having a cylindrical surface with at least onecolor-permeable zone provided with color-permeable openings, a squeegeedisposed within the screen, and two end pieces respectively fastened toopposite ends of the screen as an extension of the cylindrical surface,at least one of the end pieces of the rotary screen printing cylinderbeing configured as a connecting element, the connecting elements ofeach rotary screen printing cylinder of the system being cooperativelyengageable to interconnect the rotary screen printing cylinders.
 6. Thesystem of claim 5, wherein at least one of the connecting elements is aflange element.
 7. The system of claim 5, wherein at least one of theconnecting elements is a single piece.
 8. The system of claim 5, andfurther comprising a squeegee rod common to all the screen printingcylinders and arranged to extend axially thereto, and a squeegee elementfastened to the rod in a region of each of the screen printingcylinders.
 9. The system of claim 5, wherein the squeegee is achamber-type squeegee.
 10. The system of claim 5, wherein thecolor-permeable openings have different diameters.
 11. The system ofclaim 5, wherein at least one of the screen printing cylinders is madeof an unperforated material provided with openings only within the atleast one color-permeable zone.
 12. The system of claim 5, wherein atleast one of the screen printing cylinders is made of a mesh fabric ofpredetermined mesh width.
 13. A method for producing a system of rotaryscreen printing cylinders, comprising the steps of:providing a pluralityof rotary screen printing cylinders, each having a cylinder screen withcolor-permeable openings in at least one zone of a cylindrical surfaceof the screen; disposing a squeegee within each screen and fastening twoend pieces respectively to the ends of each screen as an extension ofthe cylindrical surface; and forming at least one end piece of eachrotary screen printing cylinder as a connecting element forinterconnecting the rotary screen printing cylinders of the system alongtheir axis.
 14. The method of claim 13, including forming at least oneconnecting element as a flange element.
 15. The method of claim 13,including forming at least one connecting element as one piece.
 16. Amethod for producing a rotary screen printing cylinder, comprising thesteps of:providing a cylindrical screen having a circular cross-sectionand formed of a mesh fabric of predetermined mesh width withcolor-permeable openings in at least one zone of a cylindrical surfaceof the screen; disposing a squeegee within the screen; fastening two endpieces respectively to opposite ends of the screen as an extension ofthe cylindrical surface; and providing at least one reinforcing elementon an entire inner circumferenced surface of the screen so as to occupyonly a portion of the circular cross-section and axial extension of thescreen for subdividing the screen into two screen chambers.
 17. A methodfor producing a rotary screen printing cylinder, comprising the stepsof:providing a cylindrical screen having a circular cross-section andwith color-permeable openings in at least one zone of a cylindricalsurface of the screen; disposing a squeegee within the screen; fasteningtwo end pieces respectively to opposite ends of the screen as anextension of the cylindrical surface; and forming at least one of theend pieces as a connecting element having means for connecting the atleast one end piece to another screen printing cylinder.
 18. The methodof claim 17, including fastening the end piece in the form of a flangeelement at the end of the screen.
 19. A method for printing securitypaper, comprising the steps of: providing a plurality of axiallyconnected rotary screen printing cylinders, each having a cylindricalscreen having a cylindrical surface with at least one zone provided withcolor-permeable openings, a squeegee disposed within the screen, and twoend pieces respectively fastened to opposite ends of the screen as anextension of the cylindrical surface, at least one of the end pieces ofeach rotary screen printing cylinder of the system being configured as aconnecting element, the connecting elements being cooperativelyengageable to interconnect the rotary screen printing cylinders;connecting together a at least two of the rotary screen printingcylinders; supplying ink to an interior of the printing cylinders;pressing the ink through the openings of the screens with the squeegee;and printing the security paper.